The effects of a pre-aversive stimulus upon the operant behavior of human subjects

Date

1966

Journal Title

Journal ISSN

Volume Title

Publisher

Abstract

The purpose of this study was to evaluate the effects of a pre-aversive stimulus followed by unavoidable shock upon human behavior. Twenty paid volunteer male college students were used as subjects. Subjects were randomly assigned to two equal groups. Ten subjects were assigned to the Avoidance Group and 10 subjects were assigned to the Positive Reinforcement Group. Each subject performed a two hour vigilance task. The Avoidance Group monitored 3 volt meters by pressing 3 corresponding push-button switches. Pointer deflections, or signals were presented on a two minute variable interval schedule. The signals remained on the meters for 5 seconds, and if they were not detected within this time, a 10, ma AC electric shock was delivered to the left leg of the subject for a duration of 150 msec. The Positive Reinforcement Group performed the same task but without the shock contingency. Instead they received a dime for every signal detected. An illuminated counter on the subjects' console kept him informed as to the number of signals detected. Signals were presented on a VI-2' schedule, and remained for 30 seconds or until detected by the subject. At the beginning of the 30th minute of the session a pre-aversive stimulus (clicker) was presented. The pre- aversive stimulus remained on for one-minute, and at the end of the minute it was terminated and an unavoidable electric shock was delivered to the subject. This procedure was repeated nine times making a total of 10 pre-aversive stimulus-shock trials. Four of the subjects in the Avoidance Group showed a significant increase in observing response rate during the pre-aversive stimulus and one subject showed a significant suppression in response rate. Five subjects did not exhibit reliable behavioral changes during the pre-aversive stimulus.. Likewise, 4 subjects in the Positive Reinforcement Group showed a significant increase in observing response rate during the pre-aversive stimulus and one subject showed a significant suppression in response rate. Five subjects did not exhibit reliable behavioral changes during the pre-aversive stimulus. In view of these findings it was concluded that the response facilitation in both groups was most likely the result of an enextinguished avoidance and escape history of the subjects, and the pre-aversive stimulus acted as a discriminative stimulus for emitting avoidance-like responses which had been effective in avoiding or escaping noxious stimuli in the past. The basal skin resistance data were generally low for both groups and due to its relatively long recovery time it did not provide any useful information relative to the effects of the pre-aversive stimulus and operant behavior. The heart rate data revealed that 7 subjects in the Avoidance Group and 9 in the Positive Reinforcement Group snowed significant heart rate increases during the pre- aversive stimulus. Comparing the heart rates between the two groups revealed no significant differences between them before the pre-aversive stimulus trials although the subjects in the Avoidance Group had slightly higher rates. When the percentage increase m heart rate during the pre-aversive stimulus trials were compared, the Positive Reinforcement Group showed a significantly greater increase than the Avoidance Group on the first trial and also on the percentage increase on all 10 pre-aversive stimulus trials. It was concluded from these analyses that the Avoidance Group was under greater 'stress' than the Positive Reinforcement Group due to the fact that the pre-aversive stimulus did not induce equal heart rate changes in the two groups. Thus it is hypothesized that increments in stress level results in non-linear increments in heart rate. That is, equal increments in stress level will result in a negatively acclerated heart rate lability curve.

Description

Keywords

Operant behavior

Citation